Following injection of a labeled amino acid or sugar into the eye of tadpoles, labeled proteins or glycoproteins are axonally transported in the optic nerve to the tectum. Significantly less radioactivity is transported to the tectum in tadpoles kept in the dark than in those kept in the light. This difference is not observed in adult frogs, which suggests that there may be a linkage between axonal transport and physiological activity that is characteristic of the immature visual system and that disappears with aging. It is proposed to analyze the differential effects of light and darkness on axonal transport in the tadpole optic nerve in order to determine: a) which axonally transported materials are involved; b) whether the effect involves a change in axonal transport or in the synthesis or turn over of the transported materials; and c) how the effect is related to changes in physiological activity of the optic axons. Sensitivity of axonal transport to darkness will also be sought in the visual system of the young of other species, in connection with the possibility that this phenomenon might be the basis for some of the functional and structural deficits produced by visual deprivation in young animals.